Alloy and manufacture



Patented Dec. 29, 1942 ALLOY AND MANUFACTURE Vsevolod Nicholas Krlvobok, Pittsburgh, Pa, as-

signor to Rustless Iron and Steel Corporation, a corporation of Delaware No Drawing. Application October 19, 1937, Se-

rial No. 169,911. In France and. Germany January 17, 1935 ll Claim.

This invention relates to austenitic chromiumnickel alloy irons and steels, and more particularly to highly heat-resistant irons and steels of the class indicated, and to articles and manufactures of the same.

Among the objects of my invention is the simple, eflicient and economical production of alloy irons and steels which are strong, ductile and readily workable, as by hot or cold rolling, forging, piercing, upsetting and the like into sheet, strip and bar stock, which readily lends itself to a variety of working and forming operations, such as machining, punching, blanking, deep-drawing and spinning to achieve a great number of products or manufacturea'such as tanks, valves, flanges, and bolts for high temperature duty, as in vats, stills, evaporator units and the like for semi-chemical uses, as in the canning, dairy, oil and photographic film industries, or as chemical calciners for the production of iron-free chemicals, such as paints and dyes, or for pans and containers for alloy' powders subjected to extremely high temperatures.

The invention accordingly consists in the combination of elements, composition of ingredients and mixture of materials, and in the articles, products and manufactures thereof, as described herein, and the scope of the application of which is indicated in the following claim.

As conducive to a clearer understanding of certain features of my invention it may be noted at this point that the austenitic chromium-nickel irons and steels (irons and steels containing approximately, 10% to 25% chromium, 7% to 15% strongly oxidizing conditions or conditions permitting direct chemical attack at these high temperatures.

One ot the outstanding objects of my invention is the production of strong, tough and ductile austenitic irons and steels of especially high heatresistant characteristics .which may be readily worked or formed into a variety of highly heatresistant products or articles of manufacture, a number of which are set forth above, particularly adapted to withstand long periods of continuous operation at high temperatures under the many oxidizing and/or corrosive conditions encountered in actual, practical use.

Referring now more particularly to the practice of my invention, ingots analyzing approximately 18% chromium, 8% nickel, 2.5% to 3.5% molybdenum, 2.5% to 3.5% copper, .03% to .4% carbon, and the balance substantially iron, with the usual percentages of silicon, manganese, sulphur and phosphorus, are produced in any suitable manner, as for example as described in the patent of Alexander L. Feild, No. 1,925,182, entitled Process for the manufacture of rustless iron; the percentages of molybdenum and copper nickel, and the balance substantially iron) are useful in the production of a wide variety of corrosion-resistant and mildly heat'resistant and hospital applications, as in cooking and;

serving utensils, common-containers and numerous appliances where permanently bright corrosion-resistant metal is desired.

These chromium-nickel irons and steels, however, may not be satisfactorily employed where long life under cont nuous operation at extremely,

high temperature is required, especially under are preferably maintained at about the same values with the sum of these percentages ranging between 5% and 7% in order to achieve maximum life at high temperatures combined with favorable working characteristics. The ingots are fashioned into blooms or billets in accordance with known methods and conveniently hot rolled into sheet bar and strip ar sizes. These bars are then annealed and pickled and, for example, cold rolled into sheet or strip of desired thickness which is subsequently made into a. roll convenient for handling.

The metal is corrosion-resistant and heatresistant, withstanding the exacting conditions of high temperature duty without grain growth, fatigue or failure, over long periods of constant use. For example, a bar of this heat-resistant iron, analyzing approximately 18% chromium, 8% nickelf2.8% molybdenum, 2.8% copper, .10% carbon, and the balance substantially iron, subjected to a stress of 8,000 pounds per square inch at a temperature of 1500 F. under oxidizing at- .mospheri'c conditions has" a life of about 490 hours. The ordinary 18-8 chromium-nickel iron, analyzing approximately, 18% chromium, 8% nickel, .07% carbon, and the balance substantially iron under like conditions of test has a life of only about 12 hours to 14 hours.

My chromium-nickel iron or steel, in addition to having a life under severe high temperature duty greatly in excess of that of heretofore known and/or used chromium-nickel irons and steels, is strong, tough, ductile and durable. The metal readily lends itself to hot or cold working, either from sheet, strip or bar stock, as bypunching, blanking, deep-drawing, spinning, upsetting, machining and the like, and subsequent welding where desired, either with the electric arc or the oxy-acetylene torch in accordance with known welding practice (employing welding rods for electric welding of the same approximate analysis as the stock welded), to form a variety of articles or products of manufacture, such as tanks, fluid valves, tubing and piping, flanges, bolts and couplings as employed in boilers, condensers, oilcracking stills and other high temperature appiications where strength and resistance to fatigue are of outstanding importance under a variety of corrosion-fostering conditions including in addition to the gases present in the normal atmosphere in and around the articles and products in use, the sulphur-bearing gases and vapors encountered in the oil stills and oil handling equipment, the mineral waters met with in boiler and condenser applications and like corrosive, embrittling and fatiguing conditions. (Welded articles or manufactures are preferably heattreated in accordance with known methods to assure the reestablishing of the austenitic condition of the metal, and thus assure maximum chemical resistance, after the welding operation is complete.)

Similarly, the sheet, strip or bar stock may be fashioned into vats, pans and other parts, as indicated above, for use in canning, dairy, photographic film, paint and dye industries, wherein high temperature duty, and especially high temperature duty under the oxidizing and corrosive effects of gases, fumes, acids, alkalies and salts, .is encountered.

' Thus, it will-be seen that there has been provided in this invention an austenitic chromiumnickel alloy and articles or manufactures produced therefrom in which the various objects herein noted, together with many thoroughly practical advantages are successfully achieved.

It will be seen that the alloy is strong, corrosionresistant, especially heat-resistant and readily workable into a wide variety of commercial parts,

articles. and accessories, a number of which are set forth above, which are particularly adapted to withstand high temperature operations over long periods of time and under the many exacting conditions of actual, practical use.

While in my invention an austenitic chromiumnickel alloy containing approximately, 18% chromium, 8% nickel, 2.5% to 3.5% molybdenum, 2.5% to 3.5% copper, .03% to .4% carbon, and the balance substantially iron, is illustratively 'described, good results are achieved where the chromium content ranges between 10% and 25%, and the nickel between 7% and 15%.

In my alloy irons and steels, as in heretofore known and/or used austenitic chromium-nickel irons and steels, carbon is not an essential ingredient.. Carbon is tolerated only because of the commercial impracticability of producing the metal without a certain amount of this ingredient being present. Ordinarily, the, carbon content amounts to about .03% to .10% although, as indicated above, this ingredient may amount to as much as .2 .3% or even .4%. As in heretofore known irons and steels of the class indicated, as low a carbon content as is commercially feasible is generally preferred.

As many possible embodiments may be made of my invention and as many changes may be made in the embodiment hereinbefore set forth, it is to be understood that all matter described herein is to be interpreted as illustrative, and not in a limiting sense.

I claim:

Wrought alloy austenitic 10 to 25 per cent chromium, '7 to 15 per cent nickel and .03 to .40 per cent carbon, stainless steel tubular articles characterized by their freedom from corrosion embrittlement and by their resistance to the wash and scour of corrosive fluids, used under conditions of high internal pressures and at high temperatures, said characteristics being produced by the inclusion in said alloy steel of 2.5 to 3.5 per cent molybdenum and 2.5 to 3.5 per cent copper.

VSEVOLOD NICHOLAS KRIVOBOK. 

